Method and system for autonomous measurement of transmission line EMF for pipeline cathodic protection systems

ABSTRACT

An active cathodic analysis protection system employs local monitors that detect the electromagnetic fields near the transmission line. This yields a set of electromagnetic field (EMF) point readings along the transmission line. From this information a three dimensional (3D) EMF field estimation is determined. EMF field estimation is used in combination with a system geometry model, which includes the transmission line geometry, the geometry of the monitors with respect to the transmission line, and the pipeline geometry.

RELATED APPLICATIONS

This application claims the benefit under 35 USC 119(e) of U.S. Provisional Application No. 62/794,772, filed on Jan. 21, 2019, which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

Pipelines are often installed in the in the same right-of-way as high voltage electrical transmission lines. These pipelines may include gas pipelines, oil pipelines, as well as pipelines that transport other liquid or gaseous substances. These pipelines are often at least partially fabricated from metal and are thus electrically conductive.

Especially when a pipeline is deployed underground and positioned roughly parallel with a high voltage transmission line, the line will induce undesired electrical currents along the metal of the pipeline, typically referred to as AC interference. And, if the pipeline exhibits a defect in its protective coating, the induced AC current may cause corrosion of the pipeline walls or fittings at the location of the defect through electrochemical reaction with adjacent soil components.

To address this problem cathodic protection systems are deployed for pipelines that run with high voltage transmission lines or at crossing points to the transmission lines. Passive protection systems rely on attaching a piece of a more electrochemically “active” metal to the pipeline. This “sacrificial metal” acts as the anode and corrodes instead of the protected metal of the pipeline. Active cathodic protection systems typically involve the impression of a DC current between the pipeline structure and a nearby anode array that biases the voltage of the pipeline negatively in order to disfavor corrosion of the pipeline. These systems are used to mitigate the corrosion impact of AC signals otherwise induced in pipeline by the transmission line.

Some have proposed active feedback cathodic protection systems that perform waveform cancellation, instead of applying a simple DC bias voltage or current. These systems detect the induced AC currents in the pipeline, possibly with a Hall effect sensor. A feedback controller then generates a current compensation signal exhibiting electrical characteristics such that the current compensation signal cancels the undesired AC current when the current compensation signal is applied to the pipe section, thereby eliminating net electrochemical exchange with the surrounding soil or water.

SUMMARY OF THE INVENTION

The present invention concerns an active cathodic protection system. It employs local monitors that detect the AC electromagnetic fields produced by the transmission line. This yields a set of electromagnetic field (EMF) point readings along the transmission line. From this information a three dimensional (3D) EMF field estimation is determined, allowing the determination of three-phase AC electric currents on the transmission line(s) producing the EMFs. EMF field estimation is used in combination with a system geometry model, which includes the transmission line geometry, the geometry of the monitors with respect to the transmission line, and the pipeline geometry. Then this estimation is applied to the pipeline itself.

The present system does not require current sensors placed near/on/around the pipeline itself. Instead, only EMF monitors must be installed in the electromagnetic “throw” of the transmission line where practical measurements are possible, and the system geometry model is generated from a survey, for example. The monitors need not contact the pipeline, nor the power line, and this can lead to a many-to-many relationship between pipelines, power lines, and sensors, in which a larger, coupled model can be created and examined. In fact, in many cases, the monitors can be installed on a completely different section of transmission line right-of-way, provided that the transmission line crosses or comes into proximity with the modeled pipeline along its path, and that the transmission line is not tapped at some intermediate point.

Typically, a server system of the protection system calculates the power flow on a given power transmission line. This data is meant to be used as input for an AC interference model (e.g. Elsyca V-PIMS), among other uses. This data can be used to inform maintenance, upgrade, construction, and design/routing decisions, and can be used in legal/regulatory interactions with regulators, electric utilities, and other utility companies. This is distinct from the use case that solely focuses reactively on sections of pipeline.

The present system can also model AC interference for multiple pipeline sections, and of multiple pipelines, that come into proximity with the monitored transmission line(s). Similarly, system can be used to measure/model and extract their individual electromagnetic field components based on deconvolution of the superimposed signals. Thus, the system can be used as part of an electromagnetic field (EMF) survey that characterizes AC impacts on entire pipeline, instead of being limited to discrete sections of individual pipelines. In addition, the system can be used to measure EMF field amplitudes and phases in a manner such that the phase order of transmission lines can be determined by calculations. This data is critical as an input parameter for AC interference modeling.

In general, according to one aspect, the invention features an AC interference or cathodic protection analysis system, comprising electromagnetic field monitors installed along a transmission line, a controller for estimating cathodic protection parameters for a pipeline, and a cathodic protection system for applying the cathodic protection to the pipeline under the control of the controller.

In embodiments, the controller estimates cathodic protection using a system geometry model. This model preferably includes a geometry of the transmission line, a geometry of the monitors, and a geometry of the pipeline. Typically, system geometry is generated by surveying along the transmission line and transverse to the transmission line. This information can be further used to generate a phase order for the transmission line.

In general, according to another aspect, the invention features a cathodic protection method. This method comprises installing electromagnetic field monitors along a transmission line; estimating cathodic protection for a pipeline based on telemetry data from the electromagnetic field monitors, and applying the cathodic protection to the pipeline.

In general, according to another aspect, the invention features a transmission line monitoring system or method comprising local monitors installed along a transmission line and a monitor server system receiving telemetry data from the local monitors and using a system geometry model to determine interference in adjacent to the transmission line.

In general, according to another aspect, the invention features a local monitor comprising a three axis magnetic field transducer, a three axis electric field transducer, a wireless data communication section, and a local controller for monitoring the three axis magnetic field transducer and the three axis electric field transducer and generating transmission line telemetry data for transmission to a monitor server system using the wireless data communication section.

Preferably, the local monitor further includes an ambient temperature sensor and an internal temperature sensor and/or a GPS receiver for receiving position and time information.

Often, the local controller provides timestamps from the GPS receiver to the and telemetry data to determine fault events.

The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale; emphasis has instead been placed upon illustrating the principles of the invention. Of the drawings:

FIGS. 1A and 1B are schematic perspective and plan views of a transmission line extending through a right-of-way along with a pipeline and showing the system for autonomous measurement of transmission line EMF for pipeline cathodic protection;

FIG. 2 is a block diagram of a local monitor 200 of the system for autonomous measurement of transmission line EMF for pipeline cathodic protection;

FIG. 3 is an entity and flow diagram showing the operation of the system including periodic sampling by the monitor server system 300 of the local monitors 200-1, 200-2, . . . 200-n for steady state monitoring;

FIG. 4 is an entity and flow diagram showing the operation of the system including periodic sampling by the monitor server system 300 of the local monitors 200-1, 200-2, . . . 200-n for fault detection;

FIG. 5 an entity and flow diagram showing how the monitors are used to perform longitudinal pipeline EMF exposure profiling;

FIG. 6 an entity and flow diagram showing how the monitors are used to perform transverse pipeline EMF exposure profiling; and

FIG. 7 shows how the monitor server system 300 processes its receive information to provide different data feeds and control the cathodic protection systems 400.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention now will be described more fully hereinafter with reference to the accompanying drawings, in which illustrative embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Further, the singular forms and the articles “a”, “an” and “the” are intended to include the plural forms as well, unless expressly stated otherwise. It will be further understood that the terms: includes, comprises, including and/or comprising, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Further, it will be understood that when an element, including component or subsystem, is referred to and/or shown as being connected or coupled to another element, it can be directly connected or coupled to the other element or intervening elements may be present.

It will be understood that although terms such as “first” and “second” are used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. Thus, an element discussed below could be termed a second element, and similarly, a second element may be termed a first element without departing from the teachings of the present invention.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

Overview

In this system and its associated method, local monitors 200 equipped with electromagnetic field (EMF) transducers, radio transceivers, and microprocessor units are installed at or near ground-level, or on existing or purpose-built poles, walls or other structures 205 in the proximity of one or more electric power transmission lines 20.

The local monitors 200 are placed in proximity to or in transmission line rights-of-ways that run near to the path(s) of pipelines 80. The centerlines 30 of the transmission lines 20 and pipelines 80 may cross, run parallel, at an angle, or have a combination of path intersection types. Pipelines may be buried, at or above grade, and may be in operation, maintenance, or under construction.

The local monitors 200 may also be installed before, in anticipation of, the construction of a pipeline or electric power line in order to create an EMF background- or reference-case study that can aid in the design and installation of pipelines and power lines.

In this context, “pipelines” may refer to those used to transport crude oil, natural gas, natural gas liquids, refined petrochemical products, fuels, agricultural (by)products, food products, water, sewage, steam, or other gaseous or liquid substance transported by pipe. Pipeline walls may be composed of any material, but emphasis is placed on metallic or conductive pipes that suffer from AC interference-induced galvanic corrosion.

The purpose of the local monitor placement is to measure the AC magnetic and electric field generated by the nearby electric power transmission lines. Then, by carefully considering the geometry of the power lines, the geometry of transmission structures and accessories (e.g. static shield wires, ground wires and ground electrodes, guy wires, etc.), and the precise locations of the local monitor(s), measurements of the magnetic and electric fields by the local monitor can be used to precisely calculate the electric currents and voltages found on the monitored transmission lines. With these electric currents and voltages in hand, along with the detailed system geometry of both the electric transmission line and the nearby pipeline, a model of electromagnetic induction and coupling (capacitive, inductive) on the pipeline is created.

FIGS. 1A and 1B illustrate the arrangement of system constructed according to the principles of the present invention and an intended environment.

A transmission line 20 contains a series of towers 22 that carry often several energized conductors 24A, 24B, 24C. These conductors 24 will often carry the different phases of the transmitted electric power. Additionally, grounded shield, neutral, or static conductors 26 are also common.

A centerline 30 characterizes the transmission line 20 i that extends longitudinally down the right-of-way 32 in which the transmission line 20 has been installed.

As noted previously, it is often common to install pipelines in this existing transmission line right-of-way 32. Such pipelines will often require cathodic protection systems 400. Such systems will have a pipeline probe 410 that makes an electrical connection to the metal of the pipeline 80. Additionally, a soil probe 420 often includes several grounding conductors 422 that make electrical connections to the soil surrounding the pipeline 80.

According to the invention, a monitor server system 300 communicates with local monitors 200 that are typically located within the transmission line right-of-way at various locations along the centerline 30 of the transmission line 20.

By examining real-time and historical EMFs, power line currents and voltages, and induced voltages on the pipeline using the present system for autonomous measurement of power line EMF for pipeline cathodic protection system 100, pipeline operators perform a number of important functions and activities.

The operators can make real-time or periodic adjustments to electronic cathodic protection systems 400 meant to provide technician safety and mitigation against galvanic corrosion, or to specify cathodic protection equipment for installation or replacement. Adjustments to cathodic protection systems/schemes may be made manually by technicians, or automatically/programmatically by the monitor server system that respond to the EMF measurements and EMF model results.

The monitor server system 300 further preferably updates corrosion models with measured data to improve understanding of corrosion risks, estimate remaining pipeline life, and draw attention to areas of the pipeline 80 that may be weakened by corrosion due to AC induction and coupling effects.

The reports from the monitor server system 300 are preferably used to expedite or delay pipeline inspections (corrosion inspections) in response to recorded EMF induction events (e.g. faults, load pattern changes, outages) and logged EMF data and calculated power line flows. This improves safety procedures and outcomes for pipeline technicians who may be exposed to induced voltages at pipeline appurtenances or exposed sections of pipeline.

As shown in FIG. 2, each local monitor 200 includes three orthogonally-oriented vector magnetic field transducers 210 (induction coil, magnetoresistive, Hall effect, or other microelectronic or microelectromechanical sensors), as well as three orthogonally-oriented electric field transducers 212 (capacitive plates or electrodes, or voltage-divider type sensors) arranged aligned and co-axially with the magnetic field transducers 210. These sensors 210, 212 are typically enclosed in a box-shaped weatherproof enclosure 220, with the orthogonal X, Y, and Z axes of the sensors 210, 212 oriented along the front, side, and top/bottom axes of the enclosure 220. The sensors 210, 212 produce analog voltage responses quickly enough to faithfully measure and characterize the 50 or 60 Hz fundamental frequency of the power line EMFs. Sensors with faster response may also be specified to allow for analysis of higher-order harmonics and transient fault events.

Also included in the enclosure 210 is a local controller 240 such as a microprocessor (e.g., a microcontroller or singleboard computer) equipped with a multi-channel analog-to-digital converter (ADC) or a single ADC with a multiplexed input. The ADC is used to transform analog voltages from the electric field transducers 212 and the magnetic field transducers 210 into digital values, which are stored into RAM 242 and/or flash memory 244. Sensor models/types with digital interface outputs may also be specified (e.g. I2C, modbus, USB, serial-interface, etc.), in which case the ADC may not be necessary.

The weatherproof enclosure 220 also houses a power supply 250, including a battery, charge controller, and voltage regulator. A solar panel or other energy harvesting unit 252 (e.g. wind turbine, piezoelectric, thermoelectric, capacitive or inductive energy harvesting device) is used to charge the battery.

Preferably, each local monitor 200 further includes additional accessory sensors that aid in the calibration and fault diagnosis and are monitored and read-out by the local controller 240. These sensors include an ambient temperature sensor and an internal temperature sensor 260 (thermometers), battery voltage sensors for determining the voltage of the battery of the power supply 250, vibration and orientation sensors (accelerometers) 262, GPS receivers 270, and tamper sensors (e.g. door open alarm). The enclosure 220 also contains a communication section, including of a cellular (e.g. GPRS) and/or satellite modem 272, one or more radio transceivers (e.g. ISM band, 900 MHz, LoRa, Bluetooth, WiFi, etc.) 274, and an antenna or array of antennas 276.

Data Analysis/Calculation

The communication section 272, 274 of each local monitor 200 is used to send telemetry data include detected and recorded sensor values and diagnostic data to the monitor server system 300 and/or to send sensor values and diagnostic data directly to the cathodic protection system 400 (machine-to-machine communications), which is programmed to respond dynamically to the sensor values (e.g. a cathodic protection station 400 that is programmed to adjust impressed voltages or currents on a nearby pipeline 80 in response to measured EMFs). When multiple EMF monitor devices are used in close proximity to each other, the communication section may be configured as a mesh network, or star topology including a base station, with which sensor values and diagnostic data from several devices might be aggregated, or logically analyzed locally based on comparison of multiple local sensor values before transmission.

The monitor server system 300 preferably includes a computer server, database, programmatic computer analysis functions, and outgoing connections to pipeline operators, pipeline-connected devices, such as cathodic protection systems 400, safety systems, and other connected automated equipment.

FIG. 3 is an entity and flow diagram showing the steady-state operation including periodic sampling by the monitor server system 300 of the local monitors 200-1, 200-2, . . . 200-n.

Each of the local monitors 200-1, 200-2, 200-n communicates with and sends their respective messages to the monitor server system 300.

The messages are typically sent and received wirelessly by a wide area network interface 310. This might be a cellular modem or an interface to a public network such as the internet. The received messages are placed in a queue 312. In step 314, this received telemetry data is associated with the various AC electric grid assets. These assets are listed in an AC electric grid infrastructure GIS database 316. Typically, the lookup is performed using the device ID, serial number, encryption key, and/or other data 282 that was sent by or employed by the local monitors 200.

From this information, the AC current and power flows for each of the monitored transmission lines are determined in step 318. Then in step 320, this information is associated with the pipelines 80 and other nearby infrastructure. This association is made by interrogating the pipeline infrastructure GIS database 322 from this information. The AC interference from the current and voltage deduced from the telemetry data on the pipelines is calculated in step 324 using the system geometry model.

The equations/physics that govern this approach are few in number. Biot-Savart law describes the vector magnetic field produced by an electric current vector at some vector distance away from the current-carrying element. Various approximations can be used to simplify the analytical solution of Biot-Savart law for high-symmetry geometries (e.g. a long straight line of current). Here, the system 300 preferably solves these equations numerically by dividing up the real line geometry into increasingly small sections and approximating each as a small straight piece of wire/conductor. Various other discrete numerical electromagnetic model solvers may also be used. This process allows the system 300 to map a magnetic field measurement at a known location to a calculated current flow on one or more conductors at other known locations. Mapping a given current flow on a known transmission line to a magnetic field at any point along the pipeline wall uses the same Biot-Savart law approach, just solved in reverse.

Mapping an incident magnetic field to the induced voltage/current on the pipeline requires application of Faraday's Law of Induction, having the system geometry model. The overhead transmission line is the source of a magnetic field, in essence the primary winding of a long and weakly coupled transformer. The secondary of this transformer is the circuit formed by the pipeline and the weakly conductive earth/soil that surrounds it. The earth/soil part is required to form a return path for any induced current so that the pipeline/earth form a current-carrying loop.

In an example configuration, the monitor 200 sends EMF sensor values to a monitor server system 300. The server 300 performs a computation that calculates the power flow on power lines proximal to the EMF sensors 210, 212 of the monitor 200 by considering the EMF sensor values (EMF amplitude, phase, vector orientation/polarization, frequency, harmonics, transients) and the relative geometry of the current- and voltage-carrying elements of the nearby power line using system geometry model. (The use of such magnetic transducers and an electric transducer to determine a net flow of current and power through a transmission line is described in U.S. Pat. Nos. 6,714,000 and 6,771,058, which are incorporated herein by reference.) The EMF model consists of analytical and numerical approaches to solving basic electrostatics equations that employ the Biot-Savart Law (magnetic field), Coulomb's Law (electric field), the Method of Image Charges (electric field), and Faraday's Law (electromagnetic induction).

In general, if the distances between the lengthwise elements of the current-carrying conductors and the EMF monitor are known precisely in the context of the system geometry model, a very accurate estimate of the line current can be computed from the EMF sensor data. When this system geometry model is preferably constructed in 3-dimensions, considering the hanging catenary shape of the conductor, the EMF field estimation of the EMF model precision is improved, and calculation of line current can be made increasingly accurately. Similar improvements are gained by using accurate site geometry measurements when computing an electric field model, which also incorporates measurements of the ground surface for the purpose of establishing an electrostatic ground plane used in the Method of Image Charges approach to computing electric field vectors. Using a dynamic EMF model that accounts for changes in conductor geometry due to changes in conductor temperature (and therefore changes in conductor sag) or wind-induced blowout or other displacements over time can also add accuracy to the EMF model above a static one-time parameterization of the EMF geometry model. Weather sensor measurements or weather data from outside sources can be used to improve measurement and model accuracy by considering changes in the moisture content and, thereby, electrical conductivity of air, soil, and vegetation caused by precipitation and subsequent effects on the propagation of electric fields.

The calculated information is stored in a pipeline AC tracking database 326. Alerts are also pushed to a data delivery modality 328. In one example, the data delivery modality implements an application programming interface 330 that supplies data to a web interface 332. In addition to data feeds 334 are also typically provided. The data feeds are used as inputs to AC interference modeling software 336 and they are also pushed to the active cathodic protection systems 400 for the various pipelines 80. In this way, detected EMF interference is used to directly control the protection systems 400.

FIG. 4 show another use of the system 100 to enable continuous monitoring for fault detection and characterization.

In general, many of the entities and steps processes are similar to that discussed in connection with FIG. 3.

AC faults in the transmission line 20 can be characterized by the system through the use of high-resolution and high-accuracy GPS timestamps from the GPS receiver 270 applied to the EMF samples and telemetry measurements collected by the local monitors 200 in step 410. When two or more monitors capture the same fault event at different locations, the fault can be localized by examining the time of detection, by reference to the timestamps and telemetry data, at the monitor sites and considering the nearby AC electric grid assets known to the system and model. Then in step 420, the fault characteristic data is associated with the adjacent pipeline infrastructure. Then, fault detection alerts can be pushed to the data delivery modality 328.

The installation of the local monitor device(s) 200 typically includes a complete site survey using standard surveying methods (e.g. laser total station, laser scanner, transit, prism, etc.) to capture and record the geometry of the monitored site. This survey yields the system geometry model that records in three dimensions: 1) the precision location and orientation of the local monitor(s) (monitory geometry), the nearby power line structure(s), conductors, insulators, crossarms, structure foundations, shield/static/ground wires (power or transmission line geometry), and ground/soil surface location (ground/soil geometry). The measurement of the conductors will capture the 3-dimensional catenary shape of the conductor. Weather observations and measurements at the time of installation will be recorded. The nearby pipeline path will be surveyed during this process to also be a part of the system geometry model, including survey measurement of any above-ground appurtenances to yield the pipeline geometry. In cases where pipelines are fully buried, and thus not measurable using standard survey equipment, pipeline operators can provide engineering and design drawings and documentation that include the shape, material composition, burial depth, path, and appurtenance details about the pipeline(s) under consideration for the monitoring project.

FIG. 5 shows how the monitors 200 are used to perform longitudinal pipeline EMF exposure profiling based on these survey geometry data sources and the system geometry model.

In addition to the local monitors 200-1, 200-2 being installed in the right-of-way 32 along the centerline 30 of the transmission line 20, a mobile monitor 200-M is loaded onto a mobile monitoring platform 510 in step 512. This platform 510 could take a number of different forms. It could be an aerial or terrestrial robot. Examples include an unmanned aerial vehicle (UAV) or a self-driving car or other vehicle. In another example it is a pipeline pig. In still other examples, the mobile monitor 200-M is mounted on a truck or carried by a human along the transmission line right-of-way 32.

The mobile platform 510 then carries the mobile monitor 200-M along the right-of-way, in step 514. At the same time information is received from the local monitors 200-1, 200-2 in step 516. As shown in step 518, this information includes the detected AC EMF information, the GPS position and GPS time stamps, the orientation and motion of the mobile monitor 200-M and, over the profiling process, its elevation and ambient temperature.

It is important to note that the fixed locations of the local monitors 200 provide control measurements of the power line EMF. This is required because the line current flows can change over the duration of the survey process as noted in association with step 516.

All of this information is provided to the monitor server system 300 in step 518. In step 520, from this information, the monitor server system 300 analyzes the EMF location and orientation data from the mobile monitor 200-M and the fixed local monitors 200 to assess the pipeline EMF exposure at each location along its length.

FIG. 6 shows how the monitors 200 are used to perform transverse pipeline EMF exposure profiling. In this process, shares many of the steps discussed in connection with FIG. 5. But now, the mobile monitor 200-M travels across the power line right-of-way in step 610. As a result, in the final step 620, the monitor server system 300 provides an analysis of the EMF measurements surveyed it locations to determine the cross-sectional EMF profile. This is used for determining the phase order of the monitored overhead circuits and specifically which of the conductors 24A, 24B, 24C carry which of the phases.

FIG. 7 shows how the monitor server system 300 processes its received information to provide different data feeds and control the cathodic protection systems 400.

In more detail, the local measurements are made by from the local monitors 200. This includes the three-dimensional AC magnetic field, the three-dimensional AC electric field and any diagnostic sensor data in step 710. In addition, weather information is also accumulated in step 712.

This information (710, 712) is received by the central processor 714 of the monitor system server 300. It further accesses the site server data 716. This includes the pipeline geometry, the power line geometry, the EMF monitor geometry, and the ground soil geometry and other soil information.

The local data and the survey data are fed into an EMF geometry model 720.

In general, after the monitor server system has computed the current and voltage phasors (mathematical representations of the amplitude and phase angle offset of the power flow components), the same geometric EMF model can be used to compute the EMF amplitude and phase incident on a nearby pipeline, also in 3-dimensions where accurate survey data are available from the system geometry model. The EMFs produced by the several conductors of a typical 3-phase circuit can be modeled independently, and conductors associated with multiple nearby 3-phase circuits can also be computed independently. The EMF model can be extended to calculate induced EMFs on multiple pipelines, and can be applied to complex pipeline intersections or paths that include turns, corners, appurtenances, valves, PIG insertion points, etc.

In more details, the results are calculated and the current and voltage transmitted on the power line are resolved in step 722. Specifically, the current, voltage and dynamic geometry of the conductors 24 is determined. This is used in the EMF geometry model to map the power line current and voltage to the EMF levels that are incident on the pipeline and other equipment in step 724. This information is placed into a message packet 726 along with the raw EMF sensor data 710, the weather data 712, the calculated transmission currents and voltages 730, and the pipeline impressed EMF is induced currents and voltages 732. This is stored to the database 740 and provided to the customers 742. Finally, the information is sent to the cathodic protection systems 400 in step 744.

In summary, by considering the incident EMFs on a pipeline 80 in detail, induced voltages and currents on the pipeline can be computed. With the induced voltages and currents, pipeline corrosion models can be updated or parameterized, and active cathodic protection systems can be adjusted manually or automatically to provide optimally-efficient and effective protection from galvanic corrosion. In addition, real-time information about induced voltages and currents can be used by inspection and maintenance crews to improve safety procedures and outcomes (fewer and less-severe shock hazards) for crews that may come into electrical contact with the pipeline.

By analyzing EMF data over longer periods of time, and especially considering the incidence of transient faults, lightning strikes, flashovers or other rapid spikes of extremely high voltage or current, pipeline asset managers can update corrosion models and mitigation strategies. This may result in expedited inspection, maintenance, or replacement of pipeline pipe, fittings, hardware, appurtenances, or may justify extended operation of the asset with fewer inspections, maintenance, or replacement events in cases where observed EMF exposure has been lower than design expectations.

While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims. 

What is claimed is:
 1. A cathodic protection system, comprising: electromagnetic field monitors installed along a transmission line; a controller for estimating cathodic protection for a pipeline based on telemetry data from the electromagnetic field monitors; and a cathodic protection system for applying the cathodic protection to the pipeline under the control of the controller.
 2. The system as a claimed in claim 1, wherein the controller estimates cathodic protection using a system geometry model.
 3. The system as a claimed in claim 2, wherein the system geometry model includes a geometry of the transmission line, a geometry of the monitors, and a geometry of the pipeline.
 4. The system as a claimed in claim 2, wherein a longitudinal pipeline EMF exposure profile is generated based on survey geometry data sources and the system geometry model.
 5. The system as a claimed in claim 1, further comprising generating a phase order for the transmission line.
 6. A cathodic protection method, comprising: installing electromagnetic field monitors along a transmission line; estimating cathodic protection for a pipeline based on telemetry data from the electromagnetic field monitors; and applying the cathodic protection to the pipeline with a cathodic protection system.
 7. The method as a claimed in claim 6, further comprising estimating cathodic protection using a system geometry model.
 8. The method as a claimed in claim 7, wherein the system geometry model includes a geometry of the transmission line, a geometry of the monitors, and a geometry of the pipeline.
 9. The method as a claimed in claim 7, further comprising generating the system geometry model by surveying along the transmission line and transverse to the transmission line. or generating the system geometry model by surveying along a pipeline right-of-way and transverse to the pipeline right-of-way.
 10. The method as a claimed in claim 6, further comprising generating a phase order for the transmission line.
 11. A transmission line monitoring system, comprising: local monitors installed along a transmission line; a monitor server system receiving telemetry data from the local monitors and using a system geometry model to determine interference in adjacent to the transmission line.
 12. A transmission line monitoring method, comprising: Detecting magnetic fields and electric fields along a transmission line with local monitors installed in a right-of-way of the transmission line; telemetry data from the local monitors and using a system geometry model to determine interference in adjacent to the transmission line.
 13. A local monitor comprising: a three axis magnetic field transducer; a three axis electric field transducer; a wireless data communication section; and a local controller for monitoring the three axis magnetic field transducer and the three axis electric field transducer and generating transmission line telemetry data for transmission to a monitor server system using the wireless data communication section.
 14. The local monitor of claim 13, further comprising an ambient temperature sensor and an internal temperature sensor.
 15. The local monitor of claim 13, further comprising a GPS receiver for receiving position and time information.
 16. The local monitor of claim 13, wherein the local controller provides timestamps from the GPS receiver with the telemetry data to the monitor server system to determine fault events.
 17. The local monitor of claim 13, wherein the monitor server system localizes the fault events using the timestamps and the telemetry data.
 18. A transmission line monitor method, comprising: detecting a magnetic field near a transmission line; detecting an electric field near the transmission line; generating transmission line telemetry data for wireless transmission to a monitor server system. 